An optical shutter described in Non-patent document 1: Ceramics, vol. 26 (1991), No. 2, pp. 139-143 is known as an optical device using the Kerr effect of an electro-optical element, and the device uses PLZT as an electro-optical element. Furuuchi Chemical Corporation sells “PLZT High-speed Optical Shutter,” the principle of which is the same as above. Referring to FIG. 1, an outline will be given on the optical shutter. The optical shutter is configured such that an electro-optical element 8 is put between a polarizer 11 and an analyzer 12, the electro-optical element 8 being configured such that a structure of electrode 82-PLZT 81-electrode 82 is repeatedly arranged in an area irradiated with a light beam 10. The polarizer 11 and the analyzer 12 are arranged such that their respective transmitted polarized light beams form an angle of 90 degrees, and the electro-optical element 8 is placed such that the direction of its electrode forms an angle of 45 degrees with the polarizer 11 or with the analyzer 12.
In the following, a principle on which a device having the above structure works as an optical shutter will be described. PLZT, which has the Kerr effect, is an isotropic crystal and is not birefringent when no voltage is applied. Accordingly, in a state where no voltage is applied, linearly polarized light transmitted through the polarizer 11 is not changed in polarization by the electro-optical element 8 comprising PLZT and cannot pass through the analyzer 12, so the shutter becomes the OFF state. On the other hand, when a voltage is applied, the PLZT element having the Kerr effect shows birefringence in the direction of the electric field and in the direction perpendicular thereto. Accordingly, if a voltage is applied which makes a phase difference of 180 degrees between a polarized light component in the direction of the electric field and that in the direction perpendicular thereto (half-wave voltage), linearly polarized light transmitted through the polarizer 11 rotates 90 degrees and becomes capable of passing through the analyzer 12. This is the ON state. As mentioned above, turning on/off the half-wave voltage allows light to be turned on/off.
The product has the plurality of structures of electrode 82-PLZT 81-electrode 82 repeatedly arranged in an area irradiated with light, so that the interelectrode distance can be made smaller than that for a structure of one set of electrode 82-PLZT 81-electrode 82, and the drive voltage is reduced to near 70 V.
A laser recording apparatus of JP-A-2000-85183 has an optical shutter part configured with the polarizer 11, the electro-optical element 8 comprising PLZT, and the analyzer 12, as in the case of the “PLZT High-speed Optical Shutter.” A schematic diagram is shown in FIG. 2. In this case, a condenser lens 7 is placed in front of the electro-optical element 8, and the electro-optical element 8 is placed in a focal position of the condenser lens 7. Consequently, an interelectrode distance between parallel electrodes 82 putting PLZT therebetween can be made small, and lower-voltage drive is realized without producing an increase in loss.